Rheological Properties of Soft Extensible Animal Tissue in Both Living and Excised States

Author: Chu, Billie Mae

Year: 1970

Degree: Dissertation (Ph.D.)

Advisor: Wayland, J. Harold

Committee Member: Unknown, Unknown

Option: Aeronautics

DOI: 10.7907/48T9-AD89

Abstract

A mechanical characterization, over a wide range of response, of a particular soft extensible animal tissue, the mesentery of the cat, is presented. The structure of the mesenteric tissue is made up of a complicated array of components and the mechanical response is influenced not only by local factors, but also by adjustments of higher control centers of the animal. Certain individual aspects of the response of living mesenteric membrane per se have been studied and contrasted with (1) membrane strongly influenced by or containing large blood vessels, (2) excised membrane and (3) membrane after circulatory collapse and accompanying sustained gut contraction.

A freely floating segment of mesentery exists in a state of

tension which can be demonstrated by making an incision through the plane of the mesentery. A technique has been developed to determine the magnitude of this tension and also the corresponding stretch which is designated here as the initial configuration length. The tension level in the tissue at the initial configuration length is not unique but can vary significantly according to the activity of the components of the membrane per se as well as the state of the gut and the large blood vessels. The most nearly unique length of the tissue which can be detected by these experimental methods is a relaxed length determined by excising a piece of tissue of known dimensions and measuring the freely floating (in a physiologic solution) dimensions to which the tissue relaxes. There is no marked material anisotropy in the plane of the membrane, i.e. the two principal dimensions in the plane of the mesentery do not vary by more than five percent even with wide history variations just prior to excision.

The temperature of the test preparation was monitored during

the course of the tests and maintained at the level of the core temperature of the animal. Since this temperature could drop as much as three or four °C as a result of the anesthesia, the influence of temperature variations on the force-stretch response of the tissue was studied and was found to be less significant than the influence of mechanical degradation in successive loading cycles.

A theoretical characterization that correlates rather well with

the data of the loading curves for the various tissues has been proposed. The limitations and assumptions incorporated in this treatment have been discussed and when appropriate additional experimental data are procured then the analytical treatment can likewise be extended to a more adequate characterization.

Photographic materials on pp. 53, 54, 55, 56, 58, 59, 60, 61,

63, 64, 66, 67, 71, 72, 83, 89, 90 and 93 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered.

Files